A satellite navigation system comprises a network of Earth-orbiting (space-based) satellites that provide time and location information to electronic receivers at or near the Earth. More specifically, the satellites in a satellite navigation system transmit radio signals along a line-of-sight that, when received by an electronic receiver, enable the electronic receiver to determine its location (e.g., longitude, latitude, and altitude) to within a range (e.g., a few yards, meters, etc.)
A satellite navigation system with global coverage is sometimes referred to as a global navigation satellite system (GNSS). As of April 2013, the United States NAVSTAR Global Positioning System (GPS) and the Russian Globalnaya navigatsionnaya sputnikovaya sistema (GLONASS) are the only fully globally operational GNSSs. However, China is in the process of expanding its regional Beidou navigation system into a global navigation system by 2020, while the European Union's Galileo positioning system is a GNSS in an initial deployment phase. Several other countries, including India, France, and Japan are in the process of developing regional navigation systems.
Satellite navigation systems may include the transmission of encrypted satellite signals (typically reserved for governmental use) and non-encrypted satellite signals (typically available for civilian use). A known problem with the use of non-encrypted signals is the potential for a “spoofing” attack. The goal of a spoofing attack is to provide a receiver with misleading/incorrect information.